Smari Mourad, Hamdi Rihab, Prado-Gonjal Jesús, Cortés-Gil Raquel, Dhahri Essebti, Mompean Federico, García-Hernández Mar, Schmidt Rainer
CICECO, Aveiro Institute of Materials, Department of Materials and Ceramic Engineering, University of Aveiro, 3810-193 Aveiro, Portugal.
Phys Chem Chem Phys. 2020 May 28;22(20):11625-11636. doi: 10.1039/d0cp00794c. Epub 2020 May 14.
Magnetoimpedance spectroscopy was carried out on phase-separated LaCaMnO polycrystalline manganites. The LaCaMnO powder was synthesized following an adapted sol-gel route. Structural and magnetic data showed the signs of phase coexistence of ferromagnetic (FM) Pnma and charge-ordered antiferromagnetic (CO-AFM) P2/m phases. Magnetization vs. temperature (M vs. T) measurements revealed several magnetic transitions from the high temperature paramagnetic (PM) to an FM phase upon cooling (PM-FM) at ≈240 K, FM-AFM (≈170 K) and AFM-FM (≈100 K). Magnetic field (H)-dependent impedance spectroscopy data were collected from sintered pellets and fitted with an equivalent circuit model to separately analyze the different dielectric contributions from the grain boundary (GB) and the grain interior bulk areas. This allowed separating the GB and bulk magnetoresistance (MR), which was shown to amount to a maximum of ≈80% for both GB and bulk at H = 10 T near the metal-insulator transition (MIT) at ≈100 K. The GB resistance was found to be larger than the bulk resistance by a factor of ≈3, which implies that the direct current (DC) resistance and DC MR are dominated by contributions from the GBs. The magnetocapacitance (MC) effects detected were all found to be small below ≈3%, including in the presence of a CO phase.
对相分离的LaCaMnO多晶锰酸盐进行了磁阻抗谱研究。采用改进的溶胶-凝胶法合成了LaCaMnO粉末。结构和磁性数据显示出铁磁（FM）Pnma相和电荷有序反铁磁（CO-AFM）P2/m相共存的迹象。磁化强度与温度（M vs. T）测量结果表明，在冷却过程中，从高温顺磁（PM）相到FM相发生了几次磁转变（PM-FM，约240 K）、FM-AFM（约170 K）和AFM-FM（约100 K）。从烧结片收集了磁场（H）依赖的阻抗谱数据，并使用等效电路模型进行拟合，以分别分析晶界（GB）和晶粒内部体区域的不同介电贡献。这使得能够分离出GB磁电阻和体磁电阻（MR），结果表明，在约100 K的金属-绝缘体转变（MIT）附近，当H = 10 T时，GB和体的磁电阻最大值均约为80%。发现GB电阻比体电阻大≈3倍，这意味着直流（DC）电阻和直流磁电阻主要由GB的贡献主导。检测到的磁电容（MC）效应在约3%以下都很小，包括在存在CO相的情况下。
